This specification relates to user authentication using access codes.
A secured system is a system that limits access in one or more ways. An access code, such as a password or a personal identification number (PIN), is a commonly used security measure for verifying the identity of a user requesting access to a secured system. A password can be entered using a keyboard, and a PIN can be entered using a PIN pad. However, the security of the system may be threatened by an attacker using techniques such as shoulder surfing, keyboard sniffing, and capturing images of the user in order to observe the user entering the access code. Examples of common techniques used to improve the security of a system include not displaying the access code on the display screen or obscuring each character of the access code using asterisks or bullets as the access code is being entered by the user, using a sophisticated display that prevents viewing past certain angles, and surrounding a keypad with a shield to limit its view to bystanders.